It is perhaps the most iconic image of the 20th century: man landing on the moon, planting an American flag and saying those famous words: "…one small step for man; one giant leap for mankind."

It was an incredible feat. So incredible that many found it hard to believe at the time.

Val Germann, president of the Central Missouri Astronomical Association, said his own grandmother was a skeptic.

"It didn't resonate with her or mean that much to her. She said, 'I don't think that really happened."

"I said, 'Oh they did [walk on the moon]. I know it's hard to believe but they did.'"

Germann, 59, has spent a lifetime studying space: He taught astronomy for more than 20 years at Missouri's Columbia College before retiring. For years he has fielded questions about moon landing conspiracies from curious students, but an online poll conducted earlier this month by Britain's Engineering and Technology magazine was the last straw.

"That is what really made me angry. I'm going, 'This stuff is still going around?'"

The poll claimed that 25 percent of British people "don't believe the Apollo 11 moon landing." Germann decided to prepare a PowerPoint presentation debunking the theories of the moonwalk naysayers and present it on Monday, the 40th anniversary of the Apollo 11 moon landing. He's expecting more than 100 people to show up.

"What's going to seal it is the new lunar reconnaissance mission," Germann said. Click HERE to learn more about the images Apollo left behind.

How Many Truly Believe the Moon Landing Was a Hoax?

For the majority of people in the U.S., there's no doubt that the moon landing happened. Just six percent of Americans think the government staged the Apollo moon landings according to a 1999 Gallup poll, the most recent data available. A similar poll by Time/CNN, conducted in 1995, also revealed that six percent believe the moon landings were faked.

NASA's mistake also caught the attention of Nashville filmmaker Bart Sibrel, one of today's most vocal skeptics decrying government-sponsored moon fakery. He claims the tapes weren't accidentally erased because "they long ago disassembled the machine that could play or record them" and is currently working on a book based on his 2002 documentary, "A Funny Thing Happened on the Way to the Moon."

Several years ago NASA responded to the public's conspiracy fascination by asking Jim Oberg, a former space engineer and the author of 10 books about space flight, to write a book for teachers, challenging the "evidence" presented by moonwalk skeptics who claim NASA faked all six manned lunar landings. But the project was cancelled in 2002 due to political pressure. Opponents suggested the money spent to hire Oberg would be a waste, and the project would end up acknowledging, and therefore lending some degree of credibility, to a small group of conspiracy theorists.

Hoax or Not? Challenging the Moon Landing Naysayers

That didn't stop Oberg from writing about various moon hoax claims elsewhere, stating in a 2003 Skeptical Inquirer magazine article that "The popularity of this particular myth is a heaven-sent (or actually, an 'outer-space-sent') opportunity to address fundamental issues of public understanding of technological controversies."

In that vein, let's address some of the most popular claims conspiracy theorists have made about the validity of the moon landing.

The Claim: If We Had Really Visited the Moon, We Would Be Able to Return. Why Haven't We Gone Back?

In 1970, "they canceled three [missions scheduled to fly to the moon] because of budget problems. Quite frankly the moon is giant parking lot, there's just not much there. Space is dangerous place. There's a lot of radiation. And humans become ill in low gravity. It's not comfortable -- it's not someplace you want to live," he added.

The Claim: On the Tape, the Shadows Look Translucent -- That Wouldn't Happen on the Moon. Was This Taped in a Studio with a Floodlight?

The shadows you see in NASA's film footage do seem odd, but Germann says there are several reasons why: the surface of the moon is uneven, and there's "lots of light kicking back from surface of moon."

"If they were faking the thing they would arrange it so that the shadows would look right," he said. "If it was a floodlight the shadows are wrong. The astronaut closer to the [supposed] floodlight would have a longer shadow."

The Claim: There Aren't Any Stars in the Pictures: How Can They Be in Space?

"I have taken thousands of astronomical pictures and I have to work to get pictures of stars," Germann said. "If you expose for the moon or sun then you will not get any stars."

NASA's Web site makes another point about the lighting conditions on the moon: "Astronauts striding across the bright lunar soil in their sunlit spacesuits were literally dazzling. Setting a camera with the proper exposure for a glaring spacesuit would naturally render background stars too faint to see."

The Claim: There Isn't Any Wind on the Moon. The Flag Shouldn't be Rippling

Yes, it is true that there is no air or wind on the moon. Germann explained that the flag moved because the astronauts touched it, creating ripples in the fabric. The flag is attached to a metal pole. If someone were to touch the metal it would vibrate, and so would the flag.

According to the moon hoax rebuttal on the NASA Web site, "Unfurling a piece of rolled-up cloth with stored angular momentum will naturally result in waves and ripples -- no breeze required!"

The Claim: If the Apollo Landed on the Moon, Why Wasn't There a Giant Blast Crater?

Germann explained that the moon is a rock that has been compacted for millions of years. On the top it is "powdery and fluffy" but a half an inch down it's hard.

"The lower layer isn't going to blow," he said.

In addition, the moon's low gravity would have eased the impact of the shuttle.

The Claim: If the Hubble Telescope Is Up There, Why Doesn't It Take a Picture?

The moon is about 240,000 miles away from the earth, whereas the Hubble Telescope orbits approximately 380 miles above the earth.

"This I don't fault people for, it's a technical question," Germann said. "Because of the way the Hubble is operated it can't resolve an object that small.

"In one sense I guess it's good that people are interested enough to doubt [the moon landing]. It's an iconic event, it stands for a whole era. And for that reason it's important to people," Germann said.

But he has little patience for the skeptics. "To say it's a fake is an insult to the many people who worked on this and risked their lives to make it happen. That's what gives it an edge for me."